Supercharger drive for airplane cabins



Patented Oct. 28, 1947 UNITED STATES PATENT vO'FFICIE.

'SUPERCHARGER DRIVEFOR-AIRPLAN E CABINS Frank W. GodseyJr., Wilknsbnrg,Pa., assignor to Westinghouse Electric Corporation,

East

Pittsburgh, Pa., a corporation olf- Pennsylvania Application September15, 11343, Serial No. 502,497

8 Claims.

trol or regulating means for controlling the speed of the blower. Sincethe external air pressure decreases ywith increase in altitude, thespeed Vof the blower must increase as the altitude increases in order tomaintain the desired air pressure within the cabin. For this reason, thecontrol for the system must `function to change the blower speed inresponse to changes in the alti- `tude or air pressure. The control mustbekept as simpleand as light in weight as possible, however, because o'fthe space and weight limitations inherent in any aircraft equipment.

The principal object of the present invention is to provide a simplesupercharger system for airplane cabins which will automatically causethe supercharger blower to operate at the correct speed at anyaltitudefto maintain the desired pressure within the cabin.

Afurther object of the invention is to provide a supercharger system forairplane cabins in which the blower is driven by an electric motor ofspecial design, with regulating meansforcontrolling the power inputtothe motor in such a manner that the blowerfruns at the correct speedat any altitude, and which lalso includes means for limiting the speedof the motor to a predetermined maximum.

A more specific object of the invention isto provide a superchargersystem using a blower which has different torque requirements atdifferent altitudes, and having an electric motor for driving theblower, and control means, the motor and control means being so designedthat the motor has a substantially linear speed-torque characteristic,so that the motor can drive the blower at only one speed at any givenaltitude, and, in effect, the blower itselr functions as apressure-sensitive device to cause the motor to drive it at the correctspeed.

The invention will be more fully understood from the following detaileddescription, taken in connection with the accompanying drawing, inwhich:

Figs. 1 andy 2 Aare illustrative curves showing controlling `the motorso that its speed-torque `characteristic is such that it can drive the'blower ,-dltlons remain constantl decreases, however, the torquerequired to drive certain characteristics of Athe supercharger system,and

FigqS is a schematic wiring diagram showing a preferred embodiment oftheinvention.

The supercharger system of the present invention consists essentially ofa blower driven by a ,direct-current electric motor, which is preferablydirect-connected to the blower, a variable volt- -age direct-currentgenerator for supplying the motor, and a regulator for controlling thecurrent input-tothe motor.

As previously stated, the vspeed ofthe blower `vmustchangevwiththealtitude ofthe airplane in `orderto maintain `the desiredpressure'withi-n the cabin Fig. -1 shows the speed andhorse;

power input to the blower as functions of Vthe Valtitude foratypicalsupercharger system, curve /Ya being `the `speed .of Atheblower, and curve b the horsepower input, expressed in per cent of `20rthe maximum speed vand horsepower, respectively. fItwill be seen fromthis figure that the Wspeedof the blower .varies approximately indirectproportionate the altitude, .except at relatively vlowalttudes where theperformance of the su rpercharger `is of'little importance. These curves.;represent:therperformance to be. obtained, or,in other .Wordstheproblem is to provide a simple `and reliable ucontrol which'will causethe blower tooperate in the manner shown by these curves.

,The torquerequired to drive either .a Centrifvu galblower oranaxial kowblower, varies as the rare of theblower speedso long as other con- Asthe air pressure the yblower Iat any .given speed will also decrease.lllhe blower therefore has different torque requirements at differentaltitudes. The present invention takes advantage of this fact to provideaverysimplecontrol systemvby using an electric motor to drive theblower, and designing and at only theone desired speed at any givenaltitude. In this manner, the blower itself functions as apressure-sensitive device to control the speed of the motor,since thespeed at any altitude is v,determined by the torque requirements of theblower at. that particular altitude.

This v.operation is further illustrated by the curves of Fig. 2. lInthis gure, which shows the characteristics of one typical designembodying theinvention, the speed and horsepower curves of Fig. l havebeen replotted as a motor speed- ,torque curve c. This igure also shows.a family of speed-torque curves Vfor the blower corresponding todifferent altitudes. It will be observed that the required motorspeed-torque curve c is substantially a straight line, and that itintersects each of the blower speed-torque curves at only one point.Therefore, if the motor which drives the blower is designed andcontrolled so that its speed-torque characteristic is substantiallylinear, as shown by the curve c, it will drive the blower at the correctspeed, and only at that speed, at any altitude, as determined by theintersection of the motor speedtorque curve with the blower speed-torquecurve for that particular altitude.

The internal voltage in any direct-current motor is proportional to theeld ux and to the speed of rotation of the motor. Since the torque is tobe made proportional to the speed, the internal voltage of the motormust be proportional to the field flux and the torque. The torque of adirect-current motor, however, is proportional to the ux and thearmature current, so that the internal voltage must be proportional tothe armature current and the square of the iiux. It will be apparent,therefore, that the desired linear speed-torque relation can be obtainedby using a direct-current motor operating at constant current anddesigned so that the held flux is proportional to the square root of theapplied voltage. If such a motor is supplied from a variable voltagesource, with a simple regulator to maintain the current supplied to themotor constant, the desired speed-torque characteristic will be obtainedand the superg charger system will function in the desired manner.

Since the held iiux of the motor is to be a function of the appliedvoltage, a shunt wound motor must obviously be used, and since the fluxis to be proportional to the square root of the applied voltage, themagnetic circuit of the motor must be designed to saturate at a fairlylow value of applied voltage. This can be done by reducing thecross-section of magnetic material at some point or points in themagnetic circuit in any suitable manner, such as by placing thin shimsof small area under the pole pieces between the pole pieces and theframe, or by punching holes in the pole pieces, or using nonmagneticrivets in the pole pieces, or in any other desired manner. By providinga saturable magnetic iield circuit in this way, the magnetization curveof the motor can be made to have sufficient curvature to approach quiteclosely to the desired function of the voltage.

If the flux is made to vary in exact proportion to the square root ofthe applied voltage, the desired motor characteristics are obtained byoperating it on constant current, as explained above. As a practicalmatter, however, it is not always possible to give the magnetizationcurve exactly the desired shape, and equally satisfactory results areobtainable if the i'ield flux is not exactly proportional to the squareroot of the applied voltage, since, if the magnetization curveapproaches the desired function within reasonable limits, the desiredmotor characteristic can be obtained by introducing a suitable variationin the current to compensate for the departure of the magnetizationcurve from the theoretically correct shape.

Thus, in one actual embodiment of the invention, the motor design wassuch that the magnetization curve did not exactly follow thetheoretically desirable square root function of the 4 voltage, but wasactually represented by the relation dh* V where p is the eld ux and Vis the applied voltage. This function is not the desired square rootfunction of the voltage, but approaches it sufficiently closely topermit the desired speedtorque characteristic to be obtained. 'I'hecurrent required in any such case may readily be determined from thevoltage and flux relations discussed above, and in this particular casethe current I is found to be I=l05-i-1.2V.

It will be clear therefore that even though the magnetization curve ofthe motor departs somewhat from the desired proportionality of iiux tothe square root of the applied voltage, the desired motorcharacteristics are obtainable by slightly varying the current tocompensate for the departure of the magnetization curve from the desiredshape. It is to be understood, therefore, that where the eld flux isreferred to in the specification and claims as being approximatelyproportional to the square root of the applied voltage, and where thecurrent is referred to as being approximately constant, theseexpressions are intended to include those cases in which themagnetization curve approaches the desired function, although it may nothave the desired proportionality in all parts of the curve, and in whichthe current is varied somewhat from a constant value to compensate forthe departure of the magnetization curve from the theoretically requiredshape. In general, as shown by the current equation given above, thecurrent necessary to produce the desired speed-torque characteristics ofthe motor will consist of a relatively large constant component and arelatively much smaller component which is proportional to the appliedvoltage. The input current to the motor can be controlled to give thisslight variation in almost as simple a manner as constant currentcontrol would permit.

An illustrative embodiment of the invention is shown in Fig. 3. In thisfigure, the supercharger blower IIJ is driven by a direct-currentshuntwound motor II which is preferably direct-connected to the blowerI0. The motor II has a compensating winding I2, to prevent distortion ofthe ux at low voltages, and has a shunt eld winding I3.

The motor I I is supplied from a variable voltage direct-currentgenerator I4 which is preferably driven direct from the airplane engine,so as to be independent of the electrical system of the airplane,although it may be driven by any other suitable prime mover. Thegenerator I4 has a compensating winding I5 to prevent distortion of itseld flux, and has a shunt field winding I6. A switch I1 may be providedin the generator field circuit for starting and stopping the operationof the system.

The current supplied to the motor II from the variable voltage generatorI4 is controlled by a regulator I8 which controls thevoltage of thegenerator I4 to supply the desired value of current to the motor I I.The regulator I8 may be of any desired type, and has been showndiagrammatically as including a variable resistance I9 connected inseries with the generator eld winding IB. The resistance I9 iscontrolled by a regulator current coil 2D, which is connected in seriesbetween the generator I5 and the motor I I soas `to Ycarry the motorcurrent. If the motor is `designed so that its iield ux is exactlyproportional to the square root of the applied voltage, the desiredoperation of the system will be obtained lif the motor is supplied withconstant current, as explained above, and the regulator can include onlythe current coil 2i), which will adjust the variable resistance I9 tocontrol the voltage-of the generator I4 so as to maintain constantcurrent at all times.

As previously explained, however, in actual practice, it is not alwayspossible to obtain exactly the ydesired relation of the motor ux toapplied voltage, and when the magnetization curve approaches r.but doesnot coincide with the theoretically desired curve, a slight variation ofcurrent must be provided to obtain the desired performance. Sincetherequired current will consist of a-constant component and arelatively small component proportional to the voltage, the desiredcurrent regulation is easily effected by providing in the regulator I8 avoltage coil 2I which is connected, as shown, across thegeneratorvoltage. The coil 2| may either oppose the coil'20 or add toits effect, depending upon the particular conditions, and it preferablyoperates on the armature of the voltage regulator I8 in the same manneras the coil 2D, so that the resultant effect is to control the currentsupplied to the motor according to a relation such as that given abovefor one particular motor design.

Since the motor is direct-connected to the blower I0, failure of themechanical coupling might cause dangerous overspeeding of the motor,land operation of the system at a higher altitude than the maximumaltitude for which it is intended may also .cause dangerousoverspeeding, since in either case the regulator would tend to increasethegenerator Voltage to its maximum valueand thus the speed of the motorwould be increased to dangerous values. In order to prevent this, anauxiliary voltage coil 22 may be provided on the regulator I8 andconnected across the generator voltage in parallel with the coil 2|. Thevoltage coil 22 preferably operates on an auxiliary armature 23 of thevoltage regulator, which is-norrnally held in inoperative position by atension spring 24. When the generator voltage exceeds a predeterminedvalue, the coil 22 moves the armature23 against a shoulder 25 on themain armature and actuates the regulator to reduce the generatorvoltage. Since the regulator limits the maximum voltage which may -besupplied by the generator I4 in this way, it also limits the maximumspeed which the motor II can reach, and thus prevents dangerousoverspeeding in ease of loss of load on the motor or operation at ahigher altitude than the system is designed for.

The system is preferably started in operation by means of the switch I1in the generator eld circuit. It would be desirable for reasons ofsimplicity to have the motor I I solidly connected to the generator I4at all times. When the motor is at rest, however, it has very lowresistance and the generator I5 would not build up its voltage with thislow resistance load across its terminals, in effect short-circuitingthem. A starting contactor 26 is provided, therefore, to disconnect themotor II from the generator when the generator voltage is below apredetermined minimum. The contactor 26 has an operating coil 21connected across the generator voltage and a contact 28 connected in themotor armature circuit. When the generator and motor are at rest, thecontactor 26 is, of course, open. When the generator is started, `thecontactor remains open until' the generator voltage has built up to thevalue for which the contactor 26 is set, which is made high enough toinsure that the generator will build up its voltage, and at this pointthe Contactor '26 closes its contact 28 to connect the motor to thegenerator. When the contacter closes, the current inrush to the motor IIwill usually cause the regulator I8 to reduce the generator voltage inorder to bring the motor current down to its regulated Value. This dropin generator voltage will cause the contacter 26 to drop outvmomentarily, and it will reclose its contact as the generator voltageagain increases. This process may occur once or several times while theblower is coming up to speed, since the effect of the regulator I8 is tolimit the motor starting current to the value for which the regulator isadjusted. This cycling operation of the contacter 2.6, however, has noharmful effect since the power is very low during starting, and its onlyeffect is to somewhat prolong the time required for the blower to comeup to speed, but this is not undesirable since the operation of thesupercharger system at low altitudes is not important.

The operation of this system will be evident from the foregoingdescription. The motor II is designed in the manner described so thatits field ilux is a nonlinear function of the applied voltage whichapproaches proportionality to the square root of the voltage to as closea degree as is practically possible. The voltage regulator I8 controlsthe current to the motor II to an approximately constant Value, thevoltage coil 2I of the regulator introducing suilicient variation in thecurrent to compensate for the departure of the actual magnetizationcurve of the motor from the theoretically desired shape. The.speedtorque characteristic of the motor is, therefore, substantially astraight line, corresponding to the curve c of Fig. 2, and since thetorque requirements of the blower Il! are diiierent at differentaltitudes, as shown by the family of blower speedtorque curves of Fig,2, the motor can drive the blower .at one, and only one, speed at anygiven altitude. As the altitude of the airplane increases the speed ofthe blower will also increase, the operating points of the system beingrepresented by the intersections of the curve c with the blower curvesin Fig. 2. The voltage regulator I8 increases the voltage of thegenerator I4 as the blower speed increases, so that the power input tothe motor is increased while the current is kept constant orapproximately constant. Thus, in effect, the blower I0 itself acts as apressure-sensitive device to control the operation of the systern, sinceits torque requirements at any given altitude, vin connection with thespeed-torque characteristic of the motor, determine the speed at whichthe blower is driven at that altitude, In this way, a very simple andreliable supercharger drive is provided which automatically drives theblower at the correct speed at any altitude. The drive system can bemade quite light because of its simplicity, since it consistsy only ofthe generator, the motor and the voltage regulator I8. The regulator canbe of any desired type which will perform the required functions, andcan be made relatively small.

It will be apparent that the invention is capable of various modicationsand embodiments, and it is to be understood therefore that although aspecic embodiment has been shown and described for the purpose ofillustration, the invention is not limited to this particulararrangement,

but in its broadest aspects it includes all equivalent embodiments andmodifications which come within the scope of the appended claims,

I claim as my invention:

1. In a supercharger system for an airplane cabin, a blower forsupplying air to the cabin to maintain an approximately constantpressure therein, said blower having diierent torque requirements atdiiierent altitudes, and drive means for said blower, said drive meanscomprising a shunt-wound direct-current electric motor in which the eldux is approximately proportional to the square root of the appliedvoltage, a variable voltage source of direct current for said motor, andregulating means for controlling the current supplied to the motor tomaintain said current approximately constant to cause the motor to havea substantially linear speed-torque characteristic.

2. In a supercharger system for an airplane cabin, a, blower forsupplying air to the cabin to maintain an approximately constantpressure therein, said blower having diierent torque requirements atdiiierent altitudes, and drive means for said blower, said drive meanscomprising a shunt-wound direct-current electric motor in which the eldilux is approximately proportional to the square root of the appliedvoltage, a variable voltage source of direct current for said motor,regulating means for controlling the current supplied to the motor tomaintain said current approximately constant to cause the motor to havea substantially linear speed-torque characteristic, and means forpreventing the speed of the motor from exceeding a, predeterminedmaximum.

3. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower, saidmotor having a saturable magnetic eld circuit such that the field ux isa nonlinear function of the applied voltage which approachesproportionality to the square root of the applied voltage, a variablevoltage source of direct current for said motor, and regulating meansfor controlling the current supplied to the motor so that said currenthas a substantially constant component and a relatively smallercomponent which is proportional to the voltage of said source.

4. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower,

said motor having a saturable magnetic eld circuit such that the eldiiux is a nonlinear function of the applied voltage which approachesproportionality to the square root of the applied voltage, a Variablevoltage source of direct current for said motor, regulating means forcontrolling the current supplied to the motor so that said current has asubstantially constant component and a relatively smaller componentwhich is proportional to the voltage of said source, and means forlimiting the speed of the motor to a predetermined maximum.

5. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower, saidmotor having a magnetic field circuit including a section of reducedcross-sectional area such that the magnetic circuit is saturable and theeld flux is approximately proportional to the square root of the appliedvoltage, a variable voltage direct-current generator for supplyingcurrent to said motor, and regulating means for controlling the voltageof said generator to maintain the current supplied to the motorapproximately constant.

6. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower, saidmotor having a magnetic eld circuit including a section of reducedcross-sectional area such that the magnetic circuit is saturable and theeld flux is approximately proportional to the square root of the appliedvoltage, a variable voltage direct-current generator for supplyingcurrent to said motor, regulating means for controlling the voltage ofsaid generator to maintain the current supplied to the motorapproximately constant, and means for preventing the voltage of saidgenerator from exceeding a predetermined maximum.

7. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower, saidmotor having a magnetic eld circuit including a section of reducedcross-sectional area such that the magnetic circuit is saturable and thefield flux is a nonlinear function of the applied voltage whichapproaches proportionality to the square root of the applied voltage, avariable voltage direct-current generator for supplying current to saidmotor, and regulating means for controlling the voltage of saidgenerator so that the current supplied to the motor has a substantiallyconstant component and a relatively smaller component which isproportional to the voltage of the generator.

8. An electric drive system for a blower, said drive system comprising ashunt-wound directcurrent electric motor for driving the blower, saidmotor having a magnetic field circuit including a section of reducedcross-sectional area such that the magnetic circuit is saturable and theeld flux is a nonlinear function of the applied voltage which approachesproportionality to the square root of the applied voltage, a variablevoltage direct-current generator for supplying current to said motor,regulating means for controlling the voltage of said generator so thatthe current supplied to the motor has a substantially constant componentand a relatively smaller component which is proportional to the voltageof the generator, and means for preventing the voltage of the generatorfrom exceeding a predetermined maximum.

FRANK W. GODSEY, JR.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PAIL'N IS Number Name Date 1,930,513 Eames Oct. 17, 19332,306,277 Oswald Dec. 22, 1942 2,281,987 Oswald May 5, 1942 2,106,237Bush Jan. 25, 1938 2,217,364 Halford et al Oct. 8, 1940 FOREIGN PATENTSNumber Country Date 211,060 Switzerland 1940

